He suggested in an interview on Sunday that Isil had provided some of the impetus for his most recent gun purchase.

"I have a right to protect my family if someone were to come after us," he said on CBS' Face the Nation. "In fact, if Isis were to visit us or our communities at any moment, the last line of defence between Isis and my family is the ability I have to protect my family."

Mr Rubio, 44, currently polls third behind Donald Trump and Senator Ted Cruz, but many Republican strategists consider him the favourite to ultimately secure the party's nomination.

The Florida senator has made guns rights a primary tenet of his campaign. Supporters can purchase a shirt which reads: "The 2nd Amendment is not a suggestion. It is a right," via his campaign website.